1. Field of the Invention
The present invention is directed generally to the control of vibration in structures, and more particularly to the confinement of vibrational energy to selected portions of structures, removing vibrational energy from these selected portions.
2. Description of Related Art
The suppression or control of vibration has an increasing importance in the design, manufacture, operation, maintenance, precision, and safety of structures and machinery. Engineering systems are subjected to numerous disturbances from either internal or external sources of vibration. Conventional methods for reducing the effect of vibration take several forms, and may be classified into the three general categories, viz. 1) isolation. e.g. the use of rubber shock mounts, 2) absorption (redirection), and 3) suppression (dissipation).
Conventional active vibration control methods utilize sensors, signal processing, actuators, and power sources to produce forces or strains in the system that counteract the vibration or effectively increase the dissipation in a system.
Many methods have been developed for adding energy dissipating (damping) mechanisms to vibrating systems. Some of the devices for adding passive damping include pneumatic and hydraulic dashpots, fluid layer dampers, viscoelastic and constrained viscoelastic layers, internal and contact mechanical friction, particle damping, impacting masses, magnetic damping, eddy current damping, and piezoelectric dissipation.
Many of the above passive methods may also be made active by enabling the control of specific material or geometric properties of the damping mechanism. Other devices for adding active damping include active constrained layer damping and closed-loop actuator-based damping methods. Closed-loop-based damping methods include feed-back and feed-forward approaches in which sensors are used to determine the vibration state of the structure, and forces dependent upon the sensor output are applied to the structure via an actuator. These forces in turn cancel or dissipate the vibration energy in the structure. xe2x80x9cSmartxe2x80x9d materials and structures have extended the range of active, as well as passive, vibration control mechanisms, where the term xe2x80x9csmartxe2x80x9d refers to materials or structures that respond to environmental or operational conditions by altering their material, geometric, or operational properties. Such a response may be triggered both with and without additional control mechanisms (such as a sensory and feed-back loop). Examples of smart materials include piezoceramics, shape memory alloys, electrostrictive and magnetostrictive materials, and Theological and magnetological fluids.
Damping methods incorporating semi-active and hybrid approaches -have also been devised. In semi-active approaches, the passive or active damping mechanism may be included or excluded from the control mechanism of the structure based on the response of the structure. The determination of when the damping elements are active may be made in either an active or a passive manner.
Although active control methods have been shown to be effective in some limited applications, their drawbacks are emphasized by a reliance on computationally complex control algorithms, high numbers of sensors and high actuator power requirements, and continuous monitoring and feed-back or feed-forward mechanisms. These drawbacks have demonstrated the need for an alternative or additional approach to vibration control. Additionally, semi-active control techniques reduce only the requirement on continuous actuation but their development and implementation has not yet progressed as far as fully active control or passive control.
There are common features among the above methods. First, they are designed to dissipate vibrations in a reactive manner. The vibration control mechanism acts upon the vibration energy to suppress vibration. Second, these methods are all designed to be most effective in a certain frequency range. Isolators, absorbers, and dampers, whether active or passive, are tuned to a specific frequency range of interest. Active cancellation methods are also limited in their effective frequency range by the speed of signal processing and actuator response time requirements. Third, these methods are designed without regard to the distribution of vibrational energy throughout the system.
It is important for the economic operation and practical implementation of active and passive vibration control technologies that the number of controlled regions and controlling components be reduced so as to achieve the vibration control objectives more effectively and efficiently.
Therefore, there is a need for a method of controlling and dissipating vibrational energy in a system which is proactively designed into the system, and which takes account of total energy distribution throughout the system. There is also a need to expand the frequency range over which vibrational energy is controlled and dissipated. Further, economic considerations drive a need to reduce the number of controlled regions and controlling components and to reduce the complexity of active vibration control systems.
Generally, the present invention relates to a method of controlling the distribution of vibrational energy throughout a structure, a structural component, or a machine, hereafter referred to as the xe2x80x9csystemxe2x80x9d, and of dissipating that vibrational energy. The method of controlling the distribution of energy, includes selecting a confinement region in a vibrating member in which the vibrational energy is to be confined. A vibration confining device is located on the vibrating member at a determined position to define the vibration confinement region. Damping elements are concentrated in the confinement region to dissipate the vibration energy confined there.
The confinement device may be passive, active, semi active or hybrid. In an active confinement device the location of the device on the structure or the confining forces applied to the structure are actively adjustable. Additionally, the damping element may be passive, active, semi passive or hybrid.
The combination of vibration control by confinement (VCC) and the Concentration of Damping Elements (CDE) offers many advantages over conventional vibration damping methods including more effective reduction of steady-state vibrations, transient vibrations, and random vibrations, a higher vibration decay rate, the effective application of damping mechanisms to off-resonance conditions, and a reduction in the number of necessary damping elements or the amount of damping material through enhance damping performance. Moreover, vibration modes and frequencies and acoustic radiation patterns may be tailored to meet a particular application requirement.
A procedure is presented for optimizing vibration confinement in a structure to a user""s requirements. The procedure includes inputting a) structural and material specifications for the structure, b) optimization parameters related to the structure and ranges for the optimization parameters and c) vibration confinement requirements for the vibration confinement region. The vibration response for the confined and unconfined regions of the structure is calculated for different values of the optimization parameters. It is then determined, for different values of the optimization parameters, whether the vibration confinement requirements are satisfied using the calculated vibration response. Sets of optimization parameters that satisfy the vibration confinement requirements are stored and an output set of optimization parameters from the stored sets of optimization parameters is selected.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.